1. Field of the Invention
The present invention relates to a reference current generator capable of freely setting the temperature characteristic of a reference current to generate.
2. Description of the Prior Art
FIG. 1 shows a reference current generator according to a prior art. The reference current generator has a transistor Q51 whose collector current is provided as a reference current Iref. The reference current Iref is determined by a base-emitter voltage Vf of a transistor Q52 and the resistance of a resistor R11. One end of the resistor R11 is connected to the emitter of the transistor Q51 as well as to the base of the transistor Q52, and the other end of the resistor R11 is connected to a low-potential power source. When the temperature rises, the base-emitter voltage Vf of the transistor Q52 drops to decrease a current passing through the resistor R11, thereby reducing the reference current Iref. Namely, the reference current Iref has a negative temperature coefficient.
FIG. 2 shows a reference current generator according to another prior art. Transistors Q53, Q54, Q55, Q56, and Q57 form a current mirror circuit, and a reference current Iref is provided as a collector current of the transistor Q57. Namely, the reference current Iref is a current passing through a resistor R12 connected to the emitter of the transistor Q57. The reference current Iref is expressed as follows: EQU Iref=(Vf56-Vf57)/R (1)
where Vf56 is a base-emitter voltage of the transistor Q56, Vf57 is a base- emitter voltage of the transistor Q57, and R is the resistance of the resistor R12.
When the size of the emitter of the transistor Q57 is larger than that of the transistor Q56, a decrease in the base-emitter voltage Vf57 due to an increase in the temperature is larger than that in the base-emitter voltage Vf56. Accordingly, the reference current Iref expressed with the equation (1) has a positive temperature coefficient, and therefore, is increased when the temperature rises.
In this way, the reference current provided by the conventional reference current generators has a positive or negative temperature coefficient, and these conventional generators have no measures to compensate fluctuations in the reference current due to changes in the temperature. These reference current generators frequently cause malfunctions in, for example, a sense amplifier that is sensitive to a slight fluctuation in the reference current.
The conventional reference current generators have a positive or negative temperature coefficient, which is not selectable according to requirements.